1. Field of the Invention
The invention pertains to extracting hemicellulose from fiber in a low moisture process. Fiber comprising cellulose and hemicellulose, caustic and relatively low amounts of water are agitated at high speeds causing a highly fluidized state that provides substantially instantaneous extraction of the hemicellulose portion of the fiber.
2. The Prior Art
Corn fiber is comprised primarily of cellulose, hemicellulose, and trace amounts of lignin, in addition to residual starch, protein, oil and ash. Other vegetable fibers also have similar compositions, such as sago, wheat, tapioca, bagasse, other cellulose and hemicellulose containing species, and the like. Fiber can be treated with alkali to extract the majority of the hemicellulose, as well as a portion of the protein, starch, and ash. Hemicellulose has many food and industrial applications (with or without additional refinement), including as a thickener, a component of an adhesive and a tackifier, to name a few. For example, starch based corrugating adhesives of the carrier, no-carrier and carrier no-carrier type comprising added hemicellulose are described U.S. Pat. No. 5,358,559.
Hemicellulose can be extracted from cellulose by using alkali such as calcium hydroxide, potassium hydroxide, or sodium hydroxide. This method is generally referred to as aqueous extraction, which has been difficult because of the cost of using large quantities of water for reaction and the difficulty in recovering hemicellulose from water solutions due to its high viscosity and solubility. Aqueous extraction generally requires dilute reaction concentrations, typically around 10% solids content (90% liquid).
There is a need for processes involving the aqueous extraction of hemicellulose which does not require large quantities of water. Alkali extraction of hemicellulose in solutions having higher solids content than typically used would alleviate the problems in the art.
We have developed a method for treating fiber in a semi-dry reaction (i.e. moisture content less than about 60%, resulting in non-fluid material) to obtain hemicellulose. In the method, the fiber is agitated at high speeds with alkali and water in a highly fluidized state, allowing substantially instantaneous extraction of the hemicellulose portion of the fiber from an insoluble complex to a soluble semi-dry fraction. The method eliminates the need for large quantities of water to extract hemicellulose from fiber and provides for reduced processing costs, reduced level of difficulty in recovering the hemicellulose and resource conservation by reducing the amount of water needed for aqueous extraction.
In the present Specification all parts and percentages are on a weight by weight basis unless otherwise specified.